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There are several tests that can be used to assist in diagnosis. The level of symptoms may determine the order of the tests, but all tests lose their usefulness if the patient is already taking a gluten-free diet. Intestinal damage begins to heal within weeks of gluten being removed from the diet, and antibody levels decline over months. For those who have already commenced themselves on a gluten-free diet, it may be necessary to perform a re-challenge with 10 g of gluten (four slices of bread) per day over 2-6 weeks before repeating the investigations. Those who experience severe symptoms (e.g. diarrhoea) earlier can be regarded as sufficiently challenged and can be tested earlier.
Combining findings into a prediction rule to guide use of endoscopy reported a sensitivity of 100% (it would identify all the cases) and specificity of 61% (it would be incorrectly positive in 39%). The prediction rule recommends that patients with high risk symptoms or positive serology should undergo endoscopy. The study defined high risk symptoms as weight loss, anaemia (haemoglobin less than 120 g/l in females and less than 130 g/l in males), or diarrhoea (more than three loose stools per day).
Blood tests
Serology by blood test is useful both in diagnosing coeliac disease (high sensitivity of about 98%, i.e. it misses 2 in 100 cases) and in excluding it (high specificity of over 95%, i.e. a positive test is most likely confirmative of coeliac disease rather than another condition). Because of the major implications of a diagnosis of coeliac disease, professional guidelines recommend that a positive blood test is still followed by an endoscopy. A negative test may still prompt a biopsy if the suspicion remains very high; this would pick up the remaining 2% undiagnosed cases, as well as offering alternative explanations for the symptoms. As such, endoscopy with biopsy is still considered the gold standard in the diagnosis of coeliac disease.
Due to its high sensitivity, serology has been proposed as a screening measure, because the presence of antibodies would detect previously undiagnosed cases of coeliac disease and prevent its complications in those patients. Serology may also be used to monitor adherence to diet: in those who still ingest gluten, antibody levels remain elevated.
Four serological blood tests exist for coeliac disease. The most widely used ones detect an antibody of the IgA type against particular antigens in the small bowel. Older tests detected antibodies against reticulin (ARA) or gliadin (AGA), but recent evidence supports the use of the more modern tests, namely those detecting IgA antibodies against endomysium (EMA) or tissue transglutaminase (TTG). Generally, serology may be unreliable in young children, with anti-gliadin performing somewhat better than other tests in children under five. Serology tests are based on indirect immunofluorescence (reticulin, gliadin and endomysium) or ELISA (gliadin or tissue transglutaminase).
Guidelines recommend that a total serum IgA level is checked in parallel, as coeliac patients with IgA deficiency may be unable to produce the antibodies on which these tests depend ("false negative"). In those patients, IgG antibodies against transglutaminase (IgG-TTG) may be diagnostic.
Endoscopy
An upper endoscopy with biopsy of the duodenum (beyond the duodenal bulb) or jejunum is performed. It is important for the physician to obtain multiple samples (four to eight) from the duodenum. Not all areas may be equally affected; if biopsies are taken from healthy bowel, it would result in false negative results.
Most patients with coeliac disease have a small bowel that appears normal on endoscopy; however, five endoscopic findings have been associated with a high specificity for coeliac disease when all are found: scalloping of the small bowel folds (pictured), paucity in the folds, a mosaic pattern to the mucosa (described as a cracked-mud appearance), prominence of the submucosal blood vessels and a nodular pattern to the mucosa.
Until the 1970s, biopsies were obtained using metal capsules attached to a suction device. The capsule was swallowed and allowed to pass into the small intestine. After X-ray verification of its position, suction was applied to collect part of the intestinal wall inside the capsule. One much utilized capsule system is the Watson capsule. This method has now been largely replaced by fiberoptic endoscopy, which carries a higher sensitivity rate and a lower error frequency.
Pathology
The classic pathology changes of coeliac disease in the small bowel are categorized by the "Marsh classification":
* Marsh stage 0: normal mucosa
* Marsh stage 1: increased number of intra-epithelial lymphocytes, usually exceeding 20 per 100 enterocytes
* Marsh stage 2: proliferation of the crypts of Lieberkuhn
* Marsh stage 3: partial or complete villous atrophy
* Marsh stage 4: hypoplasia of the small bowel architecture
The changes classically improve or reverse after gluten is removed from the diet, so many official guidelines recommend a repeat biopsy several (4–6) months after commencement of gluten exclusion.
In some cases a deliberate gluten challenge, followed by biopsy, may be conducted to confirm or refute the diagnosis. A normal biopsy and normal serology after challenge indicates the diagnosis may have been incorrect. Patients are warned that one does not "outgrow" coeliac disease in the same way as childhood food intolerances.
Other diagnostic tests
Other tests that may assist in the diagnosis are blood tests for a full blood count, electrolytes, calcium, renal function, liver enzymes, vitamin B12 and folic acid levels. Coagulation testing (prothrombin time and partial thromboplastin time) may be useful to identify deficiency of vitamin K, which predisposes patients to hemorrhage. These tests should be repeated on follow-up, as well as anti-tTG titres.
Some professional guidelines recommend screening of all patients for osteoporosis by DXA/DEXA scanning.
Screening and case finding
There is significant debate as to the benefits of screening. Some studies suggest that early detection would decrease the risk of osteoporosis and anaemia. In contrast, a cohort studied in Cambridge suggested that people with undetected coeliac disease had a beneficial risk profile for cardiovascular disease (less overweight, lower cholesterol levels).
Clinical scenarios in which screening may be justified include type 1 diabetes, unexplained iron-deficiency anemia, Down's syndrome, Turner's syndrome, irritable bowel syndrome, lupus, and autoimmune thyroid disease.
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Important notice:
The content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other
qualified health provider with any questions you may have regarding a medical condition.
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